Polychloroprene latexes were produced by the so-called emulsion polymerization method. In the emulsion polymerization method, chloroprene or a mixture of chloroprene and a monomer copolymerizable with chloroprene is emulsified in water with an emulsifier such as rosin acid soap, sodium alkylsulfate, higher alcohol sulfate ester sodium salt, polyoxyethylene alkyl ether, alkyl amine salt, quaternary ammonium salt or polyvinylalcohol and polymerized by addition of a radical initiator such as potassium persulfate. However, the polymerization method, which generally demands a large amount of emulsifier, inhibits expression of the adhesiveness inherent to polychloroprene, thus leading to drastic deterioration of the adhesive properties and the water resistance of the adhesive obtained. For that reason, there have been many attempts to develop a method of producing a polychloroprene latex having a reduced emulsifier content.
In emulsion polymerization of chloroprene, a polymer dispersant is used in combination with various surfactants in some cases for dispersion-stabilized polymerization and for improvement in various physical properties. Such polymer dispersants are generally lower in surface activity, but many of them are characteristic for example in their dispersion, aggregation and solubilization properties. Those having a relatively lower molecular weight form micelles similarly to emulsifiers, but those having a high molecular weight, which are similar in size to that of micelles, are considered not to form micelles. In particular, metal salts of aromatic sulfonic acid formalin condensates have been used commonly as the polymer dispersants in emulsion polymerization of chloroprene and they have been used widely as dispersants with strong dispersibility.
However when a polymer dispersant, such as a metal salt of aromatic sulfonic acid formalin condensate, is used, it is needed to add it to the aqueous medium in combination with an excessive amount of a surfactant (such as a polymer having emulsifier activity), which inevitably leads to deterioration in adhesive properties of the adhesive obtained (see, for example, Patent Documents 1, 2 and 3).